From tomorrow, web users who are not already subscribers to the print editions of the two papers will have to pay £1 for a day's access or £2 for a week-long subscription.

However, as an introductory offer, any customer who registers will get access to both websites for 30 days for just £1.

News International said that the iPad edition of the Times, which costs £9.99 a month, would continue to be charged separately.

"We have been very pleased with the response from readers since the launch of the new websites for The Times and The Sunday Times in May," said Rebekah Brooks, chief executive of News International.

"The new sites showcase our award-winning journalism in a very visual way, giving readers exclusive content and interactivity so that they can get even more from the news. We believe the new sites offer real value and we look forward to continuing to invest and innovate for readers."

When News International outlined its pay strategy in March, Brooks indicated that its red-top titles, the Sun and News of the World, would also move behind a pay wall at some point.

"This is just the start," she said. "The Times and the Sunday Times are the first of our four titles in the UK to move to this new approach."

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